Carburetion systems in gas turbine engines typically include a plurality of circumferentially spaced carburetion or swirler assemblies located in a dome end of a combustor thereof. Each swirler assembly cooperates with a central fuel injector disposed coaxially upstream therefrom for mixing fuel from the injector and pressurized air from a compressor of the gas turbine engine. The swirler assembly generally includes at least one stage of swirl vanes which are effective for swirling a portion of the pressurized air and mixing this air with fuel from the fuel injector. The combined fuel and air mixture is discharged into the combustor at a selected discharge spray angle with respect to a longitudinal axis of the swirler assembly.
Examples of carburetion systems including swirler assemblies and central fuel injectors are disclosed in U.S. Pat. Nos. 3,899,884 Combustor Systems, 3,589,127 Combustion Apparatus and 3,703,259 Air Blast Fuel Atomizer, all incorporated herein by reference.
In the design of gas turbine engine combustion systems, the effective mixing of fuel and air is a major objective for obtaining more complete combustion. For example, the carburetion system should be capable of obtaining reduced levels of exhaust emissions, such as, carbon monoxide, hydrocarbons, and visible smoke.
The carburetion systems should be also capable of maintaining a predetermined discharge spray angle of the fuel and air mixture. More specifically, when the discharge spray angle is relatively wide, the fuel and air mixture is more likely to impinge upon liners of the combustor and produce hot streaks. These hot streaks are fuel rich regions which cause undesirable local overheating of the liners. Furthermore, the fuel and air mixture is subject to being cooled by the cooling airflow typically provided along the liner surface which can lead to increased exhaust emissions.
When the discharge spray angle is relatively narrow, the result is a fuel rich region located centrally within the combustor. This fuel rich region tends to cause hot streaking at an aft end of the combustor as well as increased exhaust emissions.
In a desirable carburetion system, fuel and air are effectively mixed and injected into the combustor at a predetermined and controlled discharge spray angle. However, inasmuch as the gas turbine engine operates under several modes such as idle and cruise, a typical carburetion system generally represents a compromise for obtaining adequate performance throughout the operating ranges of the gas turbine engine.
For example, varying discharge spray angles from relatively narrow to relatively wide are required throughout the operating ranges of the gas turbine engine. Inasmuch as the swirler assemblies generally comprise fixed structures, they are generally fixed for obtaining an intermediate discharge spray angle providing acceptable performance. Furthermore, for obtaining adequate altitude relight capabilities of the gas turbine engine, a relatively wide discharge spray angle is required at those swirler assemblies located near fuel ignitors of the combustion system. Wide discharge spray angles are typically provided by additional means such as are disclosed in U.S. Pat. Nos. 3,990,834 Cooled Igniter and 4,180,974 Combustor Dome Sleeve, both incorporated herein by reference.
Typical prior art swirler assemblies having central injection fuel nozzles providing fuel thereto include means for constraining axial movement of the swirler assembly while allowing radial movement thereof to accommodate differential thermal radial expansion and contraction of the members thereof. This differential radial expansion and contraction, however, causes the discharge spray angle of the swirler assembly to be translated radially and thereby can additionally cause hot streaking when the discharge impinges the liners of the combustor.
Accordingly, an object of this invention is to provide an improved carburetion assembly for a gas turbine engine.
Another object of this invention is to provide an improved carburetion assembly which reduces the likelihood of hot streaking.
Another object of this invention is to provide an improved carburetion assembly including means for controlling the discharge spray angle of a fuel and air mixture.
Another object of this invention is to provide an improved carburetion assembly wherein hot streaking due to differential thermal radial expansion and contraction of structural elements thereof is reduced.
Another object of this invention is to provide an improved carburetion assembly having improved ignition capabilities.